Thor: God of Thunder

For this achievement find a group of small enemies, wait for them to gather around you and then use ground pound (Jump and hold X).
I got it during the Meteor Swarm fight on Muspelheim but I've no doubt you can get it before then.

Probably the best place to do this is on Muspelheim on the easy difficulty level. The first time you run into the little enemies that live in pods (Scorchers) there will about half a dozen who come to attack you. They don't take much to kill.

I recommend using an area of attack melee like XXXY. I actually did this accidentally at the location listed above.These enemies are probably your best bet as they are the weakest.